This invention relates to a method and apparatus for attaching a fibrous batt of material, such as sound absorbing material, to a heat fusible plastic substrate.
Sound absorbing fibrous materials or batts are commonly attached to the inner wall of plastic interior automotive panels to absorb sound and reduce noise in the passenger compartment of automobiles. The fibrous materials deaden noises generated by vibrating parts in the automobile and give the driver and passengers a feeling of riding in a more solid, well built vehicle. Among the most commonly employed sound absorbing materials used are shotties, which are fibrous sound insulating batts made by shredding and needling scrap and/or recycled materials, typically scrap and/or recycled plastics such as polypropylene, acrylonitrile-butadiene-styrene terpolymer (ABS), polyethylene terephthalate (PET), etc. Other examples of fibrous sound absorbing materials include glass fiber, synthetic fiber, natural fiber (such as wool, cotton, etc.), and combinations thereof.
Sound absorbing fibrous materials are typically attached with adhesives to various plastic automotive interior panels, such as door panels, interior trim panels, pillar panels, headliners, dashes, lift-gate panels, visors, and the like. A disadvantage with the use of adhesives for attaching fibrous sound absorbing materials to plastic automotive interior panels is that a relatively high cycle time is required for each part, regardless of whether the adhesive is applied manually or with automated equipment. In either case, the equipment used to apply the adhesive is prone to require significant maintenance, especially on account of the tendency for plugging to occur at spray nozzles, metering orifices, and the like. Adhesives are also relatively expensive. A further disadvantage with adhesives is that there is inevitably a certain amount of adhesive material which will become air-borne during application and will pollute the immediate environment, presenting possible health concerns and requiring frequent cleaning of surfaces where air-borne adhesives accumulate.
In an effort to eliminate the use of adhesives for attaching a fibrous sound absorbing material to plastic automotive interior panels, ultrasonic welding has been employed. Ultrasonic welding techniques involve the generation of high frequency vibrations which are directed toward a location on a plastic substrate, such as an automotive body panel. The vibrations cause polymer molecules at a selected location of the plastic substrate to vibrate and heat up to the melting point of the plastic. Thereafter, the fibrous material is pressed against the melted plastic and becomes physically bound to the plastic substrate as the melted plastic cools and resolidifies. Although the use of ultrasonic welding eliminates the need for adhesives, it is a relatively slow process, particularly for larger panels in which a plurality of welds are needed to securely attach the fibrous sound absorbing material to the plastic panel. Because of the high cost of ultrasonic welding equipment, a single ultrasonic welding device is used to sequentially create a plurality of welds for a single part. As a result, cycle times are relatively high, and ultrasonic welding does not, in practice, provide a substantial cost advantage over adhesives.
Therefore, there remains a need for an economical method and apparatus for attaching a fibrous sound absorbing material to a plastic substrate without adhesives.
The invention provides an improved, economical, high speed method and apparatus for attaching a fibrous material to a plastic substrate.
The method of attaching a fibrous material to a plastic substrate involves positioning the fibrous material over a surface of the plastic substrate, and directing a stream of heated air through the fibrous material and at the surface of the plastic substrate which is under the fibrous material. The quantity of air and the temperature of the heated air are sufficient to melt the surface of the plastic substrate which is under the fibrous material. After the surface of the plastic substrate has melted, the fibrous material is pressed against the melted surface of the plastic substrate to cause the fibers of the fibrous material to become immersed in the melted plastic at the surface of the plastic substrate. After the fibers are pressed against the melted plastic, the melted surface of the plastic substrate is allowed to cool and resolidify. The fibers which were immersed in the melted plastic become embedded in the resolidified plastic, thus providing a durable physical bond between certain individual fibers of the fibrous material and the surface of the plastic substrate.
The apparatus for attaching the fibrous material to the plastic substrate includes a fixture for supporting the plastic substrate and a fibrous material disposed over at least part of a surface of the plastic substrate. The apparatus also includes a tool supported adjacent to the fixture, the tool including a workpiece-engaging surface which generally conforms with the surface of the plastic substrate, with the workpiece-engaging surface including at least one orifice in communication with a supply of heated, pressurized air. An actuator is provided for reciprocating the tool between a first position in which the workpiece-engaging surface of the tool is spaced away from the surface of the plastic substrate and away from the fibrous material overlying the plastic substrate, and a second position in which the workpiece-engaging surface of the tool compresses the fibrous material against the surface of the plastic substrate.